Printing cylinder and process of manufacturing the same



Sept. 24, 1968 H. SCHRDER 3,402,449

PRINTING CYLINDER AND PROCESS OF MANUFACTURING THE SAME Filed May 3,1965 5 Sheets-Sheet l #507s gavovder @/MW 27a/@www Sept-24,1968H.SCHRDER 3,402,449

PRINTING CYLINDER AND PROCESS OF MANUFACTURING THE SAME Filed May 5,1965 5 Sheets-Sheet 2 Pfg. 5

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United States Patent O 3,402,449 PRINTING CYLINDER AND PROCESS OFMANUFACTURING THE SAME Hans Schrder, Lengerich, Germany, assignor toWindmoller & Hulscher, Lengerich, Nordrhein-Westfalen, Germany Filed May3, 1965, Ser. No. 452,555 Claims priority, application Germany, May 8,1964, W 36,749; Nov. 16, 1964, W 37,967 12 Claims. (Cl. 29-123) ABSTRACTOF THE DISCLOSURE A self-contained hollow printing cylinder for printingmachines including at least three superimposed layers of material. Theinner layer includes a thin glass liber cylinder carrier; the middlelayer is deposited on said carrier and includes a mixture ofthermosetting plastic material and glass strands; and the third or outerlayer includes a pure thermosetting plastic material. The peripheralsurface of the outer layer is smooth.

In the manufacture of printing cylinders, such as are used in anilineprinting as carriers for the rubber printing plates, aluminium isusually employed as a material for cylinders relatively large indiameter so that the reduction in weight facilitates the manipulationwhen printing cylinders must be interchanged, as is required Wheneverthe printing pitch is changed. In spite of the reduction in weightobtained by the use of aluminium as -a material of construction, theweight of the conventional printing cylinders large in diameter is stillso heavy that two persons are often incapable of performing theinterchange because human strength is insufficient for lifting theprinting cylinders and their shafts from the bearings. Lifting gear mustbe employed so that the interchange of the printing cylinders takes avery long time and involves undesirably long interruptions inproduction.

Besides, the manufacture of the known printing cylinders is highlyuneconomical because expensive casting molds must be procured for theprinting cylinders, which must be made only from time to time and insmall quantities. One casting mold is required for each size of printingcylinders used in practice. As there is no mass production of thecylinders, these casting molds cannot be fully utilized. Besides, thekeeping of the casting molds in stock is extremely expensive. Forinstance, for various printing pitches and the corresponding printingcylinders differing in circumference by increments of one centimeter,the difference between the diameter of a given cylinder and that for thenext smaller or larger printing pitch is 3.18 mm. For the manufacture ofall conventional printing cylinders having diameters from 180-800 mm.,195 molds must thus be kept available. This large number of molds, eachof which has substantially the volume of the printing cylinder to bemade therewith, requires obviously a very large space.

Another disadvantage of the conventional manufacture of printingcylinders resides in that the bores in the cylinder end walls must befinish-turned when the cylinder has been completed to ensure an exactcentering of these bores for receiving the shaft. This additionaloperation is complicated and expensive. Finally, the known printingcylinders of aluminum must be rotationally balanced on specialrotational balancing machines when the cylinders have been completed sothat the costs of the machinery and of the manufacturing process arefurther and considerably increased.

It is an object of the invention to provide a printing cylinder whichhas such a light weight that even cylinders 3,402,449 Patented Sept. 24,1968 ICE relatively large in diameter can easily be interchanged byhand, and has much lower manufacturing costs than conventional printingcylinders of aluminum whereas it meets all requirements as to themechanical properties of printing cylinders. More particularly, it is anobject of the invention to provide a novel manufacturing process whereinthe previously required, expensive procuring and stocking of castingmolds for the various cylinder diameters is no longer necessary.

According to the invention, these objects are accomplished in that aprinting cylinder for printing machines consists according to theinvention of a hollow cylinder, which comprises essentially a thincylindrical carrier of glass liber mat or the like and thermosettingplastics material deposited on this cylindrical carrier. Such a printingcylinder has the strength required for its use, particularly when, in adevelopment of the invention, a mixture of thermosetting plasticsmaterial and chopped glass strands, with an optional admixture of quartzpowder, is deposited on the cylindrical carrier, whereas the outsideperipheral surface consists suitably of pure thermosetting plasticsmaterial in order to avoid a formation of pores. The thermosettingplastics material which is reinforced with chopped glass strands and towhich quartz powder may be admixed, if desired, is about three timeslighter than aluminum but still has an extremely high strength. Theadmixing of chopped glass strands and quartz powder serves also tominimize the shrinkage of the plastics material during curing.

Because the printing cylinders according to the invention need not becast but the plastics material is deposited in a plastic state on thecylindrical carrier, it is no longer required to provide casting moldsfor each size of printing cylinder which is used in practice but thecylindrical carrier may be separately made for each size of printingcylinder so that a stocking of casting molds is entirely superfluous.

The end walls of the hollow cylinder may also consist having acylindrical carrier of cured glass fiber mat, these reinforcing ringsmay consist of cardboard tubes, on which glass fiber mats impregnatedwith thermosetting material are wound, followed by curing.

In the process according to the invention for the manufacture ofprinting cylinders, a stiff cylindrical carrier is made, which consistsof thin, originally fiat material and has the same length and insidediameter as the printing cylinder to be made, the end Wall members ofthe cylinder are mounted, the cylindrical carrier is suspended forrotation about a horizontal axis, thermosetting plastics material, or amixture containing thermosetting plastics material, is applied to theoutside peripheral surface of the rotating cylindrical carrier, andfinally the plastics material is cured and the printing cylinder isfinish-turned or ground. As has been mentioned hereinbefore, it isparticularly desirable to apply to the peripheral surface of thecylindrical carrier initially a mixture of chopped glass strands andthermosetting plastics material and, when this layer has been cured, toapply to the outside thereof a thin layer of pu-re thermosettingplastics material. For a `rapid curing of the plastics material, astream of hot air may be directed against the rotating cylinder duringthe application of any or both layers.

The intermediate layer may be applied by spraying with a spray gun. Thespraying apparatus may comprise in known manner a device for cutting andadmixing chopped glass strands. In accordance with the invention,however, the pasty material for the interlayer may alternatively be fedto an applicator bar, which contacts the peripheral surface of thecylindrical carrier along a generatrix and which is adjustable in itsdistance from the axis of such cylindrical carrier, which bar serves forspreading the material on the cylindrical carrier. The applicator barmay be used as a doctor blade for the pure thermosetting plasticsmaterial, which is applied to the cylindrical surface by anotherapplicator. This layer consisting of pure thermosetting plasticsmaterial may be colored in any suitable manner according to theinvention.

The cylindrical carriers for the printing cylinders according to theinvention may be made particularly easily and at particularly low costsif at least two supporting discs having a suitably selected diameter andcentral bores are fitted on a shaft, a mold shell consisting ofindividual bar elements extending parallel to the shaft is formed aroundthe supporting discs, a fabric layer consisting preferably of choppedglass strands and impregnated with thermosetting plastics material iswound around the mold shell and cured, whereafter the mold is removedand the end wall members of the cylinder are mounted. In this case ithas proved particularly desirable to use channelsection bars in makingthe mold shell, which bars are fitted one into the other alternatelywith inwardly and outwardly facing bases and are held together by rubberbands or the like. In a development of the invention, the supportingdiscs may be split along a diameter and their halves may be easilydetachably connected. When the cylindrical carrier is to be removed fromthe mold, these halves can be separated from each other so that the moldcollapses and can be removed with great ease from the cured cylindricalcarrier.

In the manufacture of each reinforcing ring for particularlylight-weight printing cylinders having a cylindrical carrier of glassber mat, glass ber mat impregnated with thermosetting plastics materialmay be wound around a exible cardboard tube and this tube may be formedinto a circle corresponding to the inside diameter of the cylindricalcarrier, preferably with the aid of the supporting discs used for themanufacture of the cylindrical carrier. When the resulting reinforcingrings have been cured, they may be embedded in the cylindrical carrierby casting with thermosetting plastics material.

A further improvement may be obtained according to the invention if thecylindrical carrier is double-walled and a spacing and stiffeninginterlayer is disposed between the two walls of the cylindrical carrier.As a result of the double-walled structure of the cylindrical carrier,provided with the reinforcing interlayer, the printing cylinder has thestrength and stiffness required for its use without need for providingseparate reinforcing elements inside the cylinder, even in relativelylong cylinders. Besides, the thus improved printing cylinder will resisteven very high pressures, which could result in a slight deflectionbetween the reinforcing rings in the printing cylinders according to theembodiments described hereinbefore.

The interlayer consists suitably of spacer portions arranged to maintaina considerable spacing in the peripheral direction of the cylindricalcarrier from each other, except at the connection points. This resultsin a printing cylinder having a particularly light weight because only arelatively thin layer of thermosetting plastics material must be appliedto the double-walled cylindrical carrier, which is very light owing tothe large interstices within the interlayer. In one embodiment of theinvention, the inner wall of the cylindrical carrier is surrounded by ahelically wound cardboard tube, which has been impregnated withthermosetting plastics material and cured, and this tube carries theouter wall of the cylindrical carrier. In a particularly preferredembodiment, stilening and spacing strips extending at right angles fromthe inner wall and interconnected, preferably in a honeycomb structureare provided between the two walls of the cylindrical carrier. Theconnection of the cardboard strips in a honeycomb enables a satisfactorybending of the material out of its plane without destruction of thejoints between the cardboard strips and without endangering the rigidityof the connection between the two walls of the cylindrical carrier.

In a further development of the invention, each wall of the cylindricalcarrier may consist of glass rovings, which have been impregnated withthermosetting plastics material, helically wound in a cylindricalsurface, and cured. Each of these rovings consists of a plurality ofglass laments. The rovings may be wound by a suitable apparatus aboutthe mold which serves for the manufacture of the cylindrical carrier andenable an operation without waste, different from glass fiber mats,which must be cut to suit the circumference and length of the printingcylinder to be made.

It is also proposed according to the invention to make the end lwallmembers of the cylinder from annular discs, which are separately castfrom thermosetting plastics material, preferably reinforced with glassfibers, and after curing are bonded to the cylindrical carrier. Themanufacture of the cylindrical carrier and the casting and curing of thecylinder ends may be carried out at the same time rather than insuccession, as in the embodiments described hereinbefore, which resultsin a considerable saving of time.

Further embodiments of the invention will be explained more fully and byway of example in the following description with reference to thedrawings, in which FIG. 1 is a front elevation showing an embodiment ofa printing cylinder according to the invention,

FIG. 2 shows a coordinated side elevation,

FIG. 3 is a longitudinal sectional view showing the cylinder accordingto the invention of FIGS. l and 2 on a larger scale.

FIG. 4 is a longitudinal sectional view showing a mold designedaccording to the invention and used for manufacturing the cylinder ofFIGS. 1 to 3.

FIG. 5 is a side elevation showing the mold of FIG. 4.

FIG. 5a is an elevation of the channel section bars used in themanufacture of the mold.

FIG. 6 is a top plan view showing the mold for manufacturing the endwall ymembers of the cylinder.

FIG. 7 is a sectional view taken on line A-B of FIG. 6 and showing anannular stiffening insert.

FIG. 8 is a longitudinal sectional view showing the cylinder accordingto the invention during the manufacture of the end wall members.

FIG. 9 is a top plan view showing the cylinder of FIG. 8.

FIG. l0 is a longitudinal sectional view showing a further embodiment ofa printing cylinder according to the invention.

FIG. ll is a side elevation showing the printing cylinder of FIG. l0.

FIG. l2 is a longitudinal sectional view showing a third embodiment of aprinting cylinder according to the invention during the manufacturethereof.

FIG. 13 is a longitudinal sectional view showing the printing cylinderaccording to FIGS. l0 and 1l during its manufacture.

FIG. 14 is an elevation showing the cardboard honeycombs used in makingthe printing cylinder according to FIGS. l0, l1 and 13.

In the embodiment of a printing cylinder according to the invention asshown in FIGS. 1 to 3, the cylindrical body 101 (FIG. 1) is composed ofa plurality `of layers. The inner layer 102 (FIG. 3) is formed by aglass fiber mat impregnated with thermosetting material. Theintermediate layer 103 consists of a thermosetting material, whichcontains chopped glass strands. The outer finish layer 104 consists onlyof thermosetting material. The end walls 105 and 106 of the cylindricalbody 101 consist also of a plurality of layers, namely, an innercardboard disc 107, which is reinforced by glass fiber mats 108impregnated with thermosetting plastics material, an intermediate layer109 of thermosetting material containing chopped glass strands, and anouter finish layer 110 of pure thermosetting material. The rings 111 and112 are prefabrcated from a suitable material-plastics material ormetal-and are suitably slightly tapered internally for a close fit onthe shaft. These rings are centered in the end walls 105 and 106. Thecylindrical body 101 has a plurality of stiffening rings 113, which areadhered to the inside wall surface of the cylinder and serve asreinforcements. The number of these rings depends on the length of thecylindrical body. At least two stiffening rings 113 are provided at thetwo ends of the cylindrical body and are suitably spaced from the twoouter ends of the cylinder 101 by a distance corresponding to thethickness of the end walls 105 and 106 so that they form a backing forthe cardboard disc 107, which forms the inner layer of the end walls.The starting material for the reinforcing rings is suitably acommercially available, flexible cardboard tube, which contains areinforcing layer consisting of a glass filament band impregnated withthermosetting material.

To make the mold (FIGS 4 to 5a) which is used according to the inventionin the manufacture of the cylindrical carrier of the printing cylinderdescribed hereinbefore, a series of circular discs of wood 116 arefitted on a shaft 115 in a length which corresponds to the length of themold. To facilitate the stripping from the mold, these discs are splitand held together by adhesive tape 117. The mold shell generallydesignated with 118 in FIG. 7 comprises channel-section bars 119, Iwhichare fitted one into the other and applied around the wooden discs 116.The narrow channel-section bars 119 (see particularly FIG. 5a) enablethe formation of a rigid mold shell 118 and constitute an idealexpedient for easily making a mold of any desired diameter by adding orremoving bars 119 and using wooden discs having a suitable d1- ameter sothat it is not necessary to keep molds on stock. The mold shell is heldtogether by two rubber bands 120 and 121, which are applied around thechannel-section bars 119 at both ends of the lmold. Besides, theserubber bands 120 and 121 determine the exact length of the cylinder tobe made. A 'cellophane sheet 122 applied about the resulting moldskeleton serves as a parting layer between the mold and the cylindermaterial and prevents a contamination of the mold. A glass fiber matimpregnated with thermosetting material is wound around the mold overthe cellophane sheet 122. When the thermosetting material has cured, thetube forming the cylindrical carrier can now be stripped from the mold.For this purpose, the two rubber bands 120 and 121 are removed from themold and the split wooden discs 116 are ejected with a rod. The thrustdestroys the adhesive joints 117 so that the wooden discs 116 togetherwith the shaft 115 and the section bars 119 can easily be removed. Thecellophane sheet serving as a parting layer is then removed from theinside of the cylindrical carrier, which conslsts of the glass fiber matimpregnated with thermosetting material.

The stiffening rings 113 can then be made (see FIGS. 6 and 7). The moldto be used for making the stiffening rings 113 in the process accordingto lthe invention consists essentially of one of the split wooden discs116, wh1c h has already been used in the manufacture of the cylindricalcarrier consisting of the glass ber mat 102 impregnated withthermosetting material. The wooden disc 116 is suitably placed on ahorizontal surface. To ensure that the outside diameter of thestiffening ring 113 equals the inside diameter of the tube 102, blocks123 consisting of a suitable material and having the same thickness asthe channel-section bars 119 used in manufacturing the cylin- `dricalcarrier are applied around the wooden disc 116. A steel band 124 heldtogether by adhesive tape is then applied tightly around the blocks 123so that the band protrudes to a suitable extent the surface formed bythe wooden disc 116 and the blocks 123.. A glass filament Iband 114impregnated with thermosetting material is then wound around a fiexiblecardboard tube 113. This tube is placed along the inside of the -moldand held therein by clips 125. This ensures that the stiffening ringshave an exactly circular shape and after curing have an outside diameterwhich corresponds exactly to the inside diameter of the cylindricalcarrier 102. The stiffening lrings 113 are then fitted into the interiorof the cylinder 102 in the `desired intervals and are aligned andembedded in cast thermosetting material (FIG. 3). This ensures therequired stiffness of the cylindrical carrier 102.

To manufacture the end walls 105 and 106 (FIGS. 8 and 9), the tube 102is placed in an upright position so that, eg., the end wall 105 is castfirst and the end wall 106 thereafter. To make the end wall, a cardboarddisc 107 is provi-ded, which is impregnated with 'thermosetting materialand corresponds in diameter to the inside diameter of the tube 102. Thisdisc is placed on the stiffening ring 113, which is at the top end ofthe upright tube and is offset by the thickness of the lend wall fromthe rim of the tube 102. The cardboard disc 107 has a central opening126, which is required to enable the fitting of a shaft through the endwalls -in a subsequent stage of manufacture.

The ring 127 is tapered on its outside and is centered on the cardboarddisc 107 and adhered to the latter with thermosetting material. Thecardboard ldisc is now reinforced by a layer 108 of glass fiber mats,which is impregnated with thermosetting material. Then the intermediatelayer 109 is applied by casting. This layer consists of thermosettingmaterial mixed with quartz powder and chopped glass strands. Theadmixture of quartz powder and chopped glass strands prevents to a largeextent a shrinkage of the thermosetting plastics material during curing.In end walls having a relatively large diameter, the curing of thethermosetting material sets up higher stresses. In this case it has beenfound suitable to apply to the thermosetting material while the same isstill plastic a further glass fiber mat 128 in order to avoid thesestresses, which tend to shrink the material. For instance, when themanufacture of the end wall 105 has proceeded to this stage, the endwall 106 is similarly manufactured. When the end walls 105 and 106 havebeen cured, the rings 127 are removed. Before the casting operation,these rings were provided with :a suitable release agent. The end 'walls105 and 106 are thus formed with openings, which are closed toward theinterior of the tube 102 only by the cardboard disc 107. The diameter ofthese openings is `desirably larger by a suitable amount than theinternally tapered rings 111 and 112, which will now be cast in the endwalls.

For this purpose, the tube 102 is firmly secured to the rotatablymounted shaft 115 so that an axial displacement or radial movement ofthe tube relative to the shaft is prevented. Then the tube is adjustedto rotate exactly in a circle. For this purpose, the shaft 115 isrotated. A suitable ruler is held along the rotating tube 102 so thatany deviation from an exact circular motion can be properly recognizedand eliminated by slight blows on the tube. The adjusting of the tube102 in this stage of manufacture eliminates the need for rotationallybalancing the finished cylinder on expensive machines, which would haveto be procured for this purpose, as well as the need for finish turningthe rings 111 and 112. These rings are then adhered into the end walls105 and 106 at several points with pasty thermosetting material. vWhenthe bonds have been cured, the layers 103 and 104 (FIG. 3) are appliedto the tube 102, which consists of a glass fiber mat impregnated withthermosetting material. For this purpose, the horizontally mounted shaft]l15 and the tube 102 secured to said shaft are rotated. Thermosettingmaterial mixed with chopped glass strands is then applied to the outsideperipheral sur-face of the rotating cylindrical carrier by means of asuitable tool (not shown), which may consist, e.g., of a bar. Thisapplication is conducted so that the thermosetting material is evenlyspread on the periphery of the cylindrical carrier and is smoothed as itis being applied. To accelerate the curing of the applied thermosettingmaterial, the rotating cylindrical carrier is suitably contacted with astream of Warm air during the application of the layer.

Thelayer 103 consisting of thermosetting material mixed with glass bersis applied in this process with a high degree of uniformity. Thisassists in avoiding a noncircular rotation of the cylinder and the needfor rotationally balancing the finished cylinder. On the other hand, itis difficult to avoid blisters in this mixture. The same often hasindividual air pockets, which would result in pores if this layer werefinish-turned. For this reason it has proved desirable to apply to thelayer 103 when the same has cured a finish layer 104, which consists ofa pure thermosetting material, which is preferably slightly colored bythe addition of a suitable coloring material. This finish layer providesa perfectly homogeneous finish to the cylinder. The finish layer 104 isapplied like the layer 103 by means o-f an applicator bar and while therotating cylinder is being contacted with a stream of warm air. Thecontact with a stream of warm air accelerates the curing of the layer104 and prevents a running of liquid thermosetting material from thecylinder body.

Alternatively, the layers 103 and 104 may be applied with the aid ofknown s-praying apparatus to the rotating cylinder, which is contactedwith a flow of warm air. The spraying apparatus used for applying thelayer 103 is coupled in this case to a cutting mechanism for cuttingglass strands.

When the manufacture of the cylinder has proceeded to this stage, thecylinder is then placed in an upright position on one of its end walls105 and 106 in order to provide them also with a iinish layer 110 ofpreferably colored thermosetting material. For this purpose, an adAhesive tape or the like is tightly applied around the end wall to betreated, in order to ensure a formation of neat edges. Then thethermosetting material is cast onto the end wall. At the same time, therings 111 and 112, which were previously only adhesively held in theopenings 129 and 130, are yfirmly embedded in the cast material. Whenthe finish layer applied to the end wa'lls has cured, the adhesive tapeserving to define the edges is removed.

When the cylinder made according to the process of the invention hascompletely cured, its peripheral surface and its end walls arefinish-turned or -ground with a conventional apparatus. The end Walledges are suitably slightly rounded to protect them from damage.

A further embodiment of a printing cylinder according to the inventionis shown in FIGS. 10 and 11. This embodiment is composed of a pluralityof layers 201 to 204. The inner layer 201 consists of a glass fiber matimpregnated with thermosetting plastics material. The intermediate layer202 is formed by cardboard strips (see FIG. 14), which are alsoimpregnated with thermosetting plastics material and connected in ahoneycomb structure. The layer 203 on top of the layer 202 consists ofthe same material as the layer 201. The layers 201 to 203 form adouble-walled, cylindrical carrier. The intermediate layer 202 of thiscarrier ensures the required strength and stiffness of the cylinder. Thecylindrical carrier is provided with the outer -finish layer 204, whichis made from pure, preferably colored thermosetting material and forms asmooth, non-porous outside cylindrical surface. The end walls 205 and206 of the printing cylinder consist of a layer 207 of thermosettingplastics material reinforced with glass fibers, and also of a finishlayer 204 of pure thermosetting material in order to provide a' smooth,nonporous surface. The openings 208 and 209 are centered Cir in the endwalls 205 and 206. These openings are internally tapered and serve forreceiving a printing cylinder shaft.

To manufacture a double-walled cylindrical carrier (FIGS. 12 and 13),a'n annular disc 211 is fitted on each end of a tubular mold 210. Asthis arrangement is symmetrical, only one end of the mold is shown inFIGS. l2 and 13. The spacing of the discs 211 secured to the mold 210corresponds to the length of the cylinder to be made. Each disc may besecured to the mold, eg., by a clamp screw. The discs 211 are inwardlyrecessed to form two end faces 212 and 213 extending in the peripheraldirection of the discs and a backing surface 214 for the materialformingthe cylindrical carrier. The length of the extension is suitablychosen so as to correspond substantially to the thickness of the endwalls, which are subsequently applied. A `glass fiber mat impregnatedwith thermosetting plastics material is now wound'onto the mold tube 210between the end faces 213 of the discs 211 to form the inner layer 201of the cylindrical carrier. In the embodiment of FIG. 12, thecylindrical carrier is given a double-walled structure in that afiexible cardboard tube 215 impregnated with thermosetting plasticsmaterial is helically wound around the layer 201. A Wire netting 216 isthen stretched around the cardboard tube 215 to form a backing for theouter layer 213 of the cylindrical carrier. Just as the inner layer 201,the outer layer 203 consists of a glass fiber mat, which is impregnatedwith thermosetting plastics material and wound around the wire netting216 so that both ends of the mat lie on the backing surface 214 of thetwo discs 211 and the mat conta'cts the end face 212 of the discs.

In the embodiment shown in FIG. 13, the doublewalled structure of thecylindrical carrier is obtained in that cardboard honeycombs 217 formingthe layer 202 (FIG. 10) are wound around the layer 201 consisting ofglass fiber mat impregnated with thermosetting plastics material. As isapparent from FIG. 14, the cardboard honeycombs 217 consist of cardboardstrips 218, Which are arranged on edge and are adhered to each other atspaced points so that cells 220 are formed when the strips are expandedin the direction of the double arrow 219. When the honeycomb is woundabout the inner layer 201 of the cylindrical carrier, these cells retaintheir shape because the thermosetting plastics material is cured. As hasalready -been described with reference to the embodiment shown in FIG.12, the layer 203 consisting of glass fiber mat impregnated withthermosetting plastics material is then applied over the cardboardhoneycomb 217 forming the layer 202. The use of the cardboard honeycombsrather than a cardboard tube as an intermediate layer of thedouble-walled cylindrical carrier has the advantage that an additionalwire netting as a backing for the outer glass fiber mat layer 203 of thecylindrical carrier is not required because the glass fiber mat cancover the cells of the cardboard mats 217 without difficulty. Bothmaterials are equally suitable to impart to the cylindrical carrier therequired strength and stiffness.

When the thermosetting plastics material has been cured, the cylindricalcarrier is stripped by removing the discs 211 and pulling the mold 210.In the meantime, the end wall members 205 and 206 have been cast in aseparate operation from thermosetting plastics material reinforced withchopped glass strands. These end wall members are now applied to thecylindrical carrier and adhered to it with thermosetting plasticsmaterial so thatthey contact on the inside the end faces of the layers201, 215 and 216 (FIG. 12), or 201 and 217 (FIG. 13), defined by the endface 213 of the discs 211 whereas that portion of the layer 203 whichprotrudes beyond the inner and intermediate layers of the cylindricalcarrier overlies the outside peripheral edge of the discs.

Finally, the finish layer 204 consisting of pure thermosetting plasticsmaterial, which is preferably colored, is applied to the cylindricalcarrier and the end Walls, as has been described herenbefore. When theprinting cylinder has been cured, it is finish-turned or ground on asuitable, conventional apparatus.

The cylinder according to the invention distinguishes by an extremelylight weight. Tests have shown that the weight of this cylinder ofthermosetting plastics material reinforced with glass fibers is onlyabout one third of the weight of a comparable cylinder of aluminum sothat the diiiiculties mentioned initially hereinbefore involved in aninterchange of the printing cylinders are minimized. The specialadvantage of the manufacturing process just described residesparticularly in the fact that the mold for making the cylindricalcarrier is simple and can be made with a very small expenditure andeliminates also the problem of keeping molds on stock because for themanufacture of cylinders having a given diameter it is sufficient tokeep on stock only a set of wooden discs of the respectivediameter-these discs require only a small space-whereas the other partsrequired for the manufacture of the mold, particularly thechannel-section bars, can easily -be used in such a manner as to providefor any diameter which may be required.

What is claimed is:

1. A self-contained hollow printing cylinder for printing machinescomprising at least three radially disposed layers, the inner layercomprising a thin glass fiber cylindrical carrier impregnated withthermosetting plastic material, the middle layer comprising a mixture ofthermosetting plastic material and glass strands, said middle layerbeing deposited on said carrier, and the outer layer comprising purethermosetting plastic material.

2. The cylinder of claim 1 wherein the outer peripheral surface of saidouter layer is smoothed.

3. The cylinder of claim 1 wherein said middle layer further comprisesan admixture of quartz powder.

4. The cylinder of claim 1 further comprising an annular wall disposedat each end of said carrier, each of said walls comprising a carriermaterial, a thermo-setting plastics material laminated on said carriermaterial, and a central opening for the cylinder shaft formed in each ofsaid walls.

5. The cylinder of claim 4 further comprising a plurality of reinforcingrings secured to said carrier.

6. The cylinder of claim 5 wherein said carrier comprises a cured glassfiber mat and wherein said rings comprise a plurality of cardboardtubes, and a glass liber mat wound around said tubes, said thermosettingplastic material being impregnated in said ring glass fiber mat and saidrings being cured.

7. The cylinder of claim 1 wherein said inner and middle layers areprovided with a spacing and stitfening interlayer disposed therebetweento form inner and outer cylindrical walls.

8. The cylinder of claim 7 wherein said interlayer comprises a spacermember disposed around the peripheral surface of the inner wall of saidcarrier and lying between said walls.

9. The cylinder of claim 8 wherein said spacer member comprises acardboard tube helically wound around said inner wall, and athermosetting plastic material impregnated in said tube, said tube andlplastic material being cured.

10. The cylinder of claim 8 wherein said spacer member comprises aplurality of reinforcing and spacing strips extending at right anglesfrom said inner wall, said strips being interconnected in a honeycombarrangement.

11. The cylinderof claim 7 wherein each of said walls comprises glassrovings in which said thermosetting plastic material is impregnated,said combination then being helically wound in a cylindrical surface andcured.

12. The cylinder of claim 7 further comprising an annular disc disposedat each end of said carrier, each of said discs comprising athermosetting; plastic material from which it is cast and a plurality ofglass bers embedded in said plastic material to reinforce same, saidmaterial and fibers being cured.

References Cited UNITED STATES PATENTS 1,475,963 12/ 1923 OsterlindlOl-375 X 1,787,890 1/1931 Woodward 29-132 X 2,393,953 2/1946 Bacon29-132 X 2,597,858 5/1952 Freedlander 29-130 2,647,300 8/1953 Thomas etal 29-131 X 2,718,583 9/1955 Noland et al. 219-38 2,739,917 3/1956Schulze 156-69 3,074,111 1/ 1963 Wiltshire 18-26 3,152,387 10/1964Macleod 29-1301 LOUIS O. MAASSEL, Primary Examiner.

